Many pharmaceutical products are made by blending several powders in production quantities. Careful control is essential to ensure uniformity within a given batch and from one batch to another. A typical pharmaceutical may involve five or more ingredients in powder form. It is not uncommon for one or more of the powder ingredients to contain lumps, i.e. a quantity of the powder stuck together, that must be disintegrated to enable uniform blending with other ingredients. Often there is only one active ingredient that comprises a very small fraction of the total ingredients to be combined, typically measured in micrograms or milligrams. Unless the mixing is thorough, parts of the production batch will have an insufficient amount of active ingredient to be effective, and parts of the production batch will have an excess amount of active ingredient and could be detrimental. In many cases, when the blending is complete the powder is either compressed into tablets or filled into capsules to provide measured dose quantities.
Blending of powders is commonly done in a tumbler, a closed container that is rotated, typically end over end, to mix the multiple powder ingredients to form a homogeneous blend. A known type blender that effectively mixes powders is known as a V-blender or a double cone blender. Many tumbling blenders include an intensifier bar that is rotated at high speed within the blender. Using a tumbling blender, such as a V-blender with an intensifier bar, yields a more uniform blend than a stationary blender, such as a ribbon blender. However, even blending of a micronized active ingredient with other ingredients in a tumbling blender with an intensifier bar does not always yield a uniform blend. In some situations, a micronized active ingredient will develop a static charge and form small aggregates, or lumps, which do not break up during the blending process, even with an intensifier bar. To correct the problem of aggregated powder, the powder batch may be first blended, then removed from the blender and sifted or milled, and then re-loaded into the blender to be blended again. This multiple handling process is time consuming and generates dust from the powder ingredients.
U.S. Pat. No. 8,235,582 was issued Aug. 7, 2012 to the present inventor for a METHOD FOR ALTERNATELY SIFTING AND BLENDING POWDERS IN THE SAME OPERATION. Whereas the '582 patent teaches a useful and unique method, it has been determined that in large equipment for sifting and blending powders, e.g. typically on the order of 150 kg to 2000 kg powder capacity, it is difficult or impossible to install and remove a single piece screen and single piece paddle as described above through the cover openings in the tumbling container.